1. Field of the Invention
This invention relates to a fire alarm system, sensor and method which is capable of detecting a fire through analog sensors of temperature, smoke density, etc.
2. Related Art
Convention fire alarm systems are, in general, of an on-off type and determine a fire based on whether the sensor detection data exceeds a threshold value set in a fire detector. In this type of fire alarm system, it has been a concern to eliminate possible false fire alarming and belated fire detection. For this reason, there has been proposed an analog information system. In the system, the temperature, smoke density, CO gas concentration, etc. which have been influenced by a fire are detected by using analog sensors; the detected analog data is transmitted to a central signal station where the determination as to whether there is a fire or not is made based on such a detected data change. For the same reason, so called intelligent type fire alarm sensors have also been proposed. The intelligent type sensor determines by itself if a fire is present.
In the conventional fire alarm system or sensor, data value output from the analog sensor may be influenced by diffusing behavior of smoke and CO gas and a rise in temperature surrounding the installed portion of the sensor which is changeable because of the installation height from a floor surface. For this reason, a fire alarm system able to obtain uniform results of fire alarm determination, even if the installation heights of the respective analog sensors differ from each other, has been proposed (Japanese Patent Gazette for Laying Open No.Showa 60(1985)-157695).
However, the difference of analog output data is caused not only by the difference of the installation heights but by the difference of configurations of rooms in which the analog sensors are installed. Judging from the knowledge of the inventors of the present invention, detection data output from the analog sensor will be influenced by the areas of the supervised regions of the respective analog sensors, which are defined by walls, beams or inwardly extending projections surrounding the respective analog sensors.
Inventors of the present invention found from the result of their experiments on varying areas of a laboratory room that there was a correlation between an installed area of an analog sensor and its detection data. This means that output values of the detection data may be different from each other even if they were detected under the same fire condition, and if the data were processed uniformly, there may be failure of early fire detection and also prevention of false fire alarms. For example, due to cigarette smoke in a small room, a conventional analog smoke sensor will detect high smoke concentration; a false fire detection will more easily occur in a small area room than in a large room. In a large room it needs longer time to detect fire than in a small room because smoke will be diluted by diffusion.
Inventors have considered that the above mentioned status might show a possibility of solution of such the false fire determination problem caused from difference of outputs of analog sensors by amending detection data or threshold values of analog sensors utilizing the above mentioned correlation.